1. Field of the Invention
The present invention relates to a playing pool that is non-inflatable and has no frame and particularly to a playing pool consisting of a middle ring made from a continuous plastic sheet to connect an upper ring and a bottom sheet by thermal fusion to enhance the structural strength.
2. Description of the Prior Art
In summer time swimming and water-bound recreational activities are very popular. Beaches or swimming pools are always crowd. Take into account of time, travel distance, safety and water quality, it is not desirable to take young children to those locations to spend the summer time or take part in water-related activities. Hence many families install a foldable tray type pool that contains shallow water to enable young children to play safely inside within the visual distance of the adults.
The playing pools for children mentioned above mostly are made from a flexible and air impermeable fabric that is foldable and inflatable or non-inflatable. The inflatable playing pool generally has a double-layer wall to couple with a bottom which is non-inflatable or inflatable (with air or water). An air chamber is formed and filled with air to erect the pool to  form a cubical water containing space in the center. The non-inflatable playing pool (referring to FIG. 1) includes an upper ring 5, a middle ring 6 and a bottom sheet 7 connecting together by ultra-frequency thermal fusion. The middle ring 6 consists of a plurality of individual plastic sheet 60 (referring to FIG. 2 for the extended view). These individual sheets are formed in a trapezoid shape to mate the upper ring 5 and the bottom sheet 7, and include a narrower upper side 61, a wider lower side 62 and slant lateral sides 63. The trapezoid plastic sheet 60 is connected to the upper ring 5 and the bottom sheet 7 by thermal fusion on the peripheral sides. The two lateral sides 63 of two neighboring sheets 60 are thermally fused to become a fused connection line 64 (referring to FIG. 1). The structure of such a playing pool has the middle ring 6 formed by thermal fusion of the individual plastic sheets 60 with the upper ring 5 and the bottom sheet 7 that have different perimeters. The thermally fused portion frequently is the first location to be burst under water pressure, especially at the middle ring portion. As the middle ring 6 consists of a plurality of fused connection lines 64, its strength against water pressure is lower and the probability of bursting is greater.